Need help trying to figure out what to check next. Here's the story.

At Sebring on Sunday, the car was feeling really good.

After the second session, it started to hesitate and not run well at idle when I was leaving the track. I took it for some parade laps during lunch and it started to run better at the lower RPMs and not bog down.

I thought it may be running rich (because of the heavy gas smell), and figured that by running it easy, it was burning off the gunk that may be building up on the plugs (just a guess...I could be totally wrong).

Session 3 was good. Didn't idle great when I came off the track, but didn't really die.

Session 4...it started to break up in the mid-rpm range and would bog down a bit...then would run strong. End of session 4 when leaving the track, wanted to die at low RPMs. Took a bit to keep it running to get it on the trailer and same when I got home.

Last night, I tried to get it running to take it for a drive. It wouldn't stay running if I took my foot off the gas. At 1500+ rpms, it would stay running, but didn't sound smooth.

So tonight, I changed the spark plugs. I thought that would help solve the problem. When pulling the plugs, some of them were a lot darker than others.

Here's a picture of them lined up in the right order they would be in the motor.
http://i26.photobucket.com/albums/c105/DanBabb/Plugs.jpg

A couple are dark on one side and tan/clay colored on the other half...what's causing that?


When I was done, I tried to start it up. Still doesn't want to run. If I stay on the gas, it will run, I can let my foot off and as long as I keep it up over 1200 rpms, it will run. If I take my foot off or bring the RPMs below 1,000...it dies.

Here's everything I know about the motor. It's only got about 3-4k miles on it.

Here's everything I know about it.

Chevy SB 400
Bored .40over

Stock Crank & Rods

Pistons – Keith Black KB147 40over. 18cc/ D-cup Effective Head Volume: 18cc

Specs:
Bore: 4.125
Rod Length:5.7
Pin Diameter:0.9272
Stroke:3.75
Comp. Ht:1.43
Crank-to-Deck Clearance: 9.025
Weight Piston / Pin: 543 / 145

Compression Ratio: 64cc-10.2 with 30over. I’m a bit lower than that with 40 over
76cc chamber heads would be 9.1

Heads 3947041 K 9 8 (K 9 8 = Nov 9, 1968 Date Code)
69-70...302/350......"Right angle" casting identifier, 64cc chamber, accessory holes

Cam: unsure. It's supposed to be a short duration cam to help build torque.

Intake: Victor Jr single plane intake

Carb: Holley 750 double pumper.
Jets: Primaries ?? 77 secondaries

Plug Wires: Moroso Super 40 (I think that's what they're called. They are sleeved with a heat resistant material.

Autolite 85 plugs gapped at around .32 -.34


Any ideas?

What should the plug gap be? The old ones were around .32-.34. I've got the new ones at the same range. Is that too narrow if it's running rich? Would too much fuel at idle be killing the spark?

I'm calling the engine guy on Monday, but would like to check some things out this weekend, but don't know what to do here.

im no expert by far, but it looks like its getting to much gas. i had a problem with my power valve in my holley 750dp, it got dry rotted from sitting. it was basically dumping gas down and fouling out my plugs. maybe something happened?? my plug gaps on my 406 is set at .40. like i said, im no expert

That's what I think....but it ran ok before the track. It just smelled a bit rich when cruising on the street.

Other than messing up the plugs (which I've changed), what else would be fouled up that could cause it to not stay running now? Could the carb be gunked up from too much gas?

the guy that built my motor and the same guy that rebuilt my carb after the blown power valve, said it doesnt take much, even with the power vavle protection valve. could also got a spec of dirt or something causing the float not to seal, that would cause it to flood, check your peep hole to see if it level. i dont think the carb would be gunked up because of too much gas, get it running right and it should clean itself in time, maybe add a cleaner. how old is your carb?